Yes! I noticed this too, I really want to go with the PWA / open approach, however after a bit more research it looks like the PWA would be barely usable on mobile without their "closed APIs" a native app has :/
Will research what is the thinnest "wrapper" I can use to avoid maintaining 3 different apps.
SSI is supported by "old battle tested" servers like Apache or Nginx, there's a "new guy on the block" that I find quite promissing: Caddy[0] however it doesn't support SSI, instead they have some built-in template engine that is a bit more powerful than old SSI but can achieve the same result.
I never released a production website with SSI before, but I found it when I was searching for a more bare-metal approach to make websites; then I found Caddy's template engine and it's been more than enough for what I need.
HTML + CSS for whitespacing & viewport width + SSI | Caddy's template
That combo is more than enough for almost all the websites out there, I've 3 different sites like that and they are blazingly fast, everything served from a $4 VPS (serving about 20k views per week).
I'm not "smart enough" to calculate that acurately, but if the "cost per transaction" is high enough to get a couple of articles written about it, I won't participate into that.
*: Market as in people who may find it useful, not market as in "I would monetize it", screw that.